CN-121978247-A - Quantitative analysis method and system for chemical valence distribution of iron element in lithium iron phosphate material

CN121978247ACN 121978247 ACN121978247 ACN 121978247ACN-121978247-A

Abstract

The invention provides a quantitative analysis method and a quantitative analysis system for the chemical valence state distribution of iron element in a lithium iron phosphate material, and relates to the technical field of combined analysis. Aiming at the technical problems that ferrous ions in a lithium iron phosphate solid material are extremely easy to oxidize and the separation of the ferrous ions in a conventional chromatographic column is difficult, the invention effectively prevents valence variation in the dissolution process by utilizing an acid solvent subjected to deoxidization treatment to dissolve a sample and introducing a specific iron ion valence stabilizer under a strict inert gas protection atmosphere. Further, by adding a specific complexing agent to form a stable complex with obvious chromatographic behavior difference with iron ions in different valence states, the baseline separation of Fe 2+ and Fe 3+ on a liquid chromatographic column is realized, and high-sensitivity quantitative detection is performed by utilizing mass spectrometry. The method can accurately measure the content of trace Fe 3+ impurities and the Fe 2+ /Fe 3+ ratio in the lithium iron phosphate material, and provides a powerful tool for quality control of high-performance battery materials.

Inventors

MA SIYUAN
WANG WEIWEI
HONG YUHAO
WANG HAILONG
TIAN JINGHUA
HONG WENJING
TIAN ZHONGQUN

Assignees

嘉庚创新实验室

Dates

Publication Date: 20260505
Application Date: 20260302

Claims (10)

1.A quantitative analysis method for the chemical valence distribution of iron element in a lithium iron phosphate material is characterized by comprising the following steps: deoxidizing the non-oxidizing acid solution for dissolving the sample, and the volatile buffer salt, the pH regulator, the blank diluent and the constant volume water which are added subsequently; Under the inert atmosphere with the oxygen content less than or equal to 10 ppm, dissolving a lithium iron phosphate sample in a deoxidized non-oxidizing acid solution containing a specific complexing agent, then adding a deoxidized volatile buffer salt, adjusting the pH value to a range matched with the pH value of an eluent used for subsequent chromatographic separation, and using deoxidized constant volume water to fix the volume to obtain a sample solution to be detected containing a ferrous complex and a ferric complex; diluting the sample solution to be detected by using a blank diluent which contains volatile buffer salt and a specific complexing agent with the same concentration and is subjected to deoxidization treatment to obtain a final sample injection solution; Introducing the final sample solution into a chromatograph, and separating by adopting a strong anion exchange chromatographic column to obtain iron element chromatographic column effluent liquid with different valence states, wherein the eluent used for separation contains the volatile buffer salt and the specific complexing agent, and the pH value of the eluent is matched with that of the final sample solution; introducing the effluent of the iron element chromatographic column with different valence states into an inductively coupled plasma mass spectrometer, and detecting after eliminating multi-atomic ion interference by adopting a collision or reaction mode; And respectively constructing standard curves of ferrous iron and ferric iron, substituting the quantitative analysis results into the standard curves, and respectively obtaining the mass percent contents of ferrous iron and ferric iron in the sample through calculation.
2. The quantitative analysis method for the chemical valence distribution of iron element in a lithium iron phosphate material according to claim 1, wherein the inert atmosphere is selected from nitrogen and/or argon; preferably, the oxygen content in the inert atmosphere environment is less than or equal to 1 ppm; Preferably, the specific complexing agent is selected from any one or a combination of at least two of pyridine-2, 6-dicarboxylic acid, ethylenediamine tetraacetic acid, citric acid, diethylenetriamine pentaacetic acid and nitrilotriacetic acid; preferably, in the non-oxidizing acid solution and the sample solution to be measured after final volume fixing, the concentration of the specific complexing agent is 2.0-20.0 mmol/L, preferably 4.0-10.0 mmol/L; Preferably, the non-oxidizing acid is hydrochloric acid; Preferably, in the non-oxidizing acid solution for dissolution, the concentration of the non-oxidizing acid is 0.5-4.0 mol/L; preferably, the pH value is adjusted to be matched with the eluting solution in a range that the pH value of the solution is adjusted to be 4.0-7.0, preferably 5.0-6.0; Preferably, the reagent used for adjusting the pH value is selected from ammonia water and/or acetic acid; preferably, in the process of preparing the solution of the sample to be tested, the mass m, the volume V of the constant volume and the dilution factor D of the lithium iron phosphate sample are required to be recorded; preferably, the method of deoxidizing treatment comprises an inert gas bubbling method and/or an ultrasonic assisted deaeration method.
3. The quantitative analysis method for the chemical valence state distribution of iron element in a lithium iron phosphate material according to claim 1, wherein the chromatograph comprises an ion chromatograph or a liquid chromatograph; preferably, the strong anion exchange chromatographic column comprises hydrophilic polymer matrix filler with quaternary ammonium salt functional groups, and the specification of the strong anion exchange chromatographic column is 50-250 mm in column length range, 2.0-4.6 mm in inner diameter and 3-10 mu m in particle size.
4. The quantitative analysis method for the chemical valence distribution of the iron element in the lithium iron phosphate material according to claim 1 or 3, wherein the eluent used for separation comprises a specific complexing agent, a volatile buffer salt, a pH regulator and a solvent; preferably, the specific complexing agent in the eluent is selected from any one or a combination of at least two of pyridine-2, 6-dicarboxylic acid, ethylenediamine tetraacetic acid and citric acid, preferably pyridine-2, 6-dicarboxylic acid; Preferably, the concentration of the specific complexing agent in the eluent is 0.5-10.0 mmol/L, preferably 2.0-5.0 mmol/L; preferably, the volatile buffer salt is selected from any one or a combination of at least two of ammonium acetate, ammonium hydroxide or ammonium formate; Preferably, the concentration of the volatile buffer salt in the eluent is 20-200 mmol/L, preferably 50-100 mmol/L; Preferably, the pH adjuster in the eluent is selected from ammonia and/or acetic acid; preferably, the pH of the eluent is 5.0-7.0; Preferably, the solvent in the eluent is ultrapure water, wherein the resistivity of the ultrapure water is more than or equal to 18.2M omega cm; preferably, in the separation process, the flow rate of the eluent is 0.2-1.2 mL/min; Preferably, in the separation process, the column temperature of the chromatographic column is 20-40 ℃.
5. The quantitative analysis method for the chemical valence distribution of iron element in a lithium iron phosphate material according to claim 1, wherein the inductively coupled plasma mass spectrometer monitors the signal intensity of a main isotope m/z 56 in real time and simultaneously monitors the signal intensity of auxiliary validation ions m/z 54 and/or m/z 57; Preferably, the parameter setting of the inductively coupled plasma mass spectrometer comprises that the temperature of a rotational flow atomizing chamber of semiconductor refrigeration is 2-5 ℃, the radio frequency power of plasma is 1300-1600W, and the sampling depth is 7-10 mm.
6. The quantitative analysis method for the chemical valence state distribution of iron element in the lithium iron phosphate material according to claim 1 or 5, wherein in the quantitative analysis process by adopting the inductively coupled plasma mass spectrometer, a helium collision mode or a hydrogen reaction mode is adopted to eliminate multi-atomic ion interference generated by plasma; Preferably, in the helium collision mode, the flow rate of helium is 4.0-6.0 mL/min; preferably, in the hydrogen reaction mode, the flow rate of hydrogen is 2.0-8.0 mL/min.
7. The quantitative analysis method for the chemical valence distribution of the iron element in the lithium iron phosphate material according to claim 1, wherein the construction method of the standard curve specifically comprises the following steps: Respectively preparing a series of standard solutions of ferrous salts with different concentrations and a series of standard solutions of ferric salts with different concentrations; Sampling and analyzing a standard solution of ferrous salt and a standard solution of ferric salt under the same chromatographic and mass spectrometry conditions as a sample to be tested; And respectively constructing a ferrous iron standard curve and a ferric iron standard curve by taking the mass concentration of the iron element in the corresponding valence state as an abscissa and the chromatographic peak area in the corresponding valence state as an ordinate.
8. The quantitative analysis method for the chemical valence state distribution of iron element in the lithium iron phosphate material according to claim 7, wherein the preparation method of the standard solution of ferrous salt and ferric salt is as follows: preparing a standard stock solution of ferrous salt, and diluting the standard stock solution by using a diluent which contains a final sample injection solution, a specific complexing agent with basically consistent types and concentrations in an eluent and a volatile buffer salt and has the pH value consistent with the eluent to obtain a series of standard solutions of ferrous salt with different concentrations; Preparing a standard stock solution of ferric salt, and diluting the standard stock solution by using a diluent which contains a final sample injection solution, a specific complexing agent with basically consistent types and concentrations in an eluent and a volatile buffer salt and has the pH value consistent with the eluent to obtain a series of standard solutions of the ferric salt with different concentrations; preferably, the ferrous salt is selected from ferrous ammonium sulfate, and the ferric salt is selected from ferric chloride or ferric nitrate; Preferably, the concentration gradient of the standard solution of the ferrous salt is set in the range of 0.01-1000 mg/L, and the concentration gradient of the standard solution of the ferric salt is set in the range of 0.001-100 mg/L.
9. A quantitative analysis system for the chemical valence distribution of iron element in a lithium iron phosphate material is characterized by comprising the following components: A protective dissolving and complexing device, wherein the inside of the protective dissolving and complexing device is provided with an inert atmosphere environment with oxygen content less than or equal to 10 ppm (preferably less than or equal to 1 ppm) and is used for dissolving the lithium iron phosphate sample in a non-oxidizing acid solution containing a specific complexing agent, and fixing the volume after adding a volatile buffer salt to adjust the pH value to obtain a sample solution to be tested containing ferrous complex and ferric complex; the separation chromatograph is internally provided with a strong anion exchange chromatographic column and is provided with an eluent containing volatile buffer salt and the specific complexing agent, the pH value of the eluent is matched with that of a sample solution to be detected, and the eluent is used for processing and separating iron complexes with different valence states in the sample solution to be detected; the inductively coupled plasma mass spectrometer is provided with a collision/reaction tank and is used for receiving effluent of the iron chromatographic column with different valence states and analyzing the iron with different valence states in the sample to be tested; and the data processing unit is used for carrying out data analysis processing.
10. The quantitative analysis system for the chemical valence distribution of iron element in lithium iron phosphate material according to claim 9, wherein the separation chromatograph comprises a liquid chromatograph or an ion chromatograph; and/or the quantitative analysis system further comprises a four-way valve sample injector, wherein one passage of the four-way valve sample injector is communicated with the protective dissolving and complexing device and the chromatographic column in the separation chromatograph, and the other passage is communicated with the mobile phase storage device and the chromatographic column in the separation chromatograph; And/or a high-pressure pump is arranged between the mobile phase storage device and the chromatographic column in the separation chromatograph and used for pumping the mobile phase and then conveying the mobile phase to the chromatographic column through a four-way valve sample injector.

Description

Quantitative analysis method and system for chemical valence distribution of iron element in lithium iron phosphate material Technical Field The invention belongs to the technical field of analysis and detection of lithium ion battery materials, and particularly relates to a quantitative analysis method and a quantitative analysis system for chemical valence distribution of iron element in a lithium iron phosphate material. Background As an extremely important positive electrode material for lithium ion batteries, lithium iron phosphate (LiFePO 4, LFP) has electrochemical properties that depend to a large extent on the chemical valence distribution of the iron element in the material. Ideally, the iron in LFP should all be present as ferrous iron (Fe (II)). However, during synthetic preparation (e.g., insufficient sintering, raw material residue), storage or use of the material, small amounts of ferric iron (Fe (III)) impurities or defective phases (e.g., fePO 4、Fe2O3, etc.) are inevitably introduced or generated. The presence of these Fe (III) impurities can significantly reduce the actual specific capacity, electron conductivity, and ion diffusion rate of the material, thereby severely affecting the cycle life and rate performance of the battery. Therefore, the establishment of the method capable of accurately and sensitively simultaneously qualitatively and quantitatively analyzing the content distribution of Fe (II) and Fe (III) in the lithium iron phosphate material has important significance for optimizing the production process, improving the product quality and deeply understanding the material failure mechanism. Currently, methods for iron valence state analysis mainly include solid surface/bulk analysis techniques represented by musburg spectroscopy (M, ssbauer Spectroscopy) and X-ray photoelectron spectroscopy (XPS), and wet chemical analysis techniques represented by titration and chromatography-spectroscopy combined techniques. Although musburg spectrum and XPS can provide in-situ valence state information, the instrument is expensive, complex to operate, has high requirements on sample preparation, can only generally give a semi-quantitative relative content ratio, is difficult to meet the requirements of quick and accurate quantification in industrial production, has large error in micro-phase analysis with the content of less than 1%, and is not suitable for being used as a conventional quality control means for detecting trace Fe (III) impurities. Traditional wet chemical titration methods (e.g., potassium dichromate to determine total iron, combined with other methods to determine Fe (II)) are cumbersome to operate and are susceptible to interference from other redox species in the sample. More importantly, conventional wet analysis presents a great challenge in sample pretreatment (dissolution) in that LFP is structurally stable, and generally requires strong acid digestion at high temperatures, whereas in the presence of acidity and especially dissolved oxygen, the bulk component Fe (II) is very easily oxidized to Fe (III), resulting in a severely higher (false positive) Fe (III) assay. Although reducing agents such as ascorbic acid are often added to protect Fe (II) in the prior art, trace Fe (III) impurities originally existing in a sample are reduced to Fe (II), so that the result of Fe (III) is low and even undetectable (false negative), and the original state of the material cannot be truly reflected. In recent years, high Performance Liquid Chromatography (HPLC) or Ion Chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS) combined technology (LC-ICP-MS or IC-ICP-MS) has become a powerful tool for elemental morphology analysis due to its high separation capacity and high sensitivity. However, the technology still has significant technical bottlenecks when applied to LFP materials (1) an effective pretreatment means is lacked to dissolve LFP and simultaneously 'lock' the valence state of iron to prevent Fe (II) oxidation or Fe (III) reduction, (2) extremely high concentration phosphate ions (PO 43-) in an LFP matrix are extremely easy to form indissolvable ferric phosphate precipitates with Fe (III) under the conventional chromatographic conditions to cause chromatographic column blockage and Fe (III) signal loss, (3) strong acid dissolution liquid direct injection can cause strong fluctuation of the pH environment in the chromatographic column to damage complex stability to cause peak tailing and even separation failure, and (4) ICP-MS is severely interfered by multi-atom ions (such as 40Ar16O+) when detecting iron elements (main isotopes 56 Fe) to influence the accuracy of trace analysis. Therefore, there is a need to develop a new method for accurately and sensitively determining the form and content of Fe (II) and Fe (III) in lithium iron phosphate while preventing the change of valence state. In view of this, the present invention has been made. Disclosur